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All dimensions are in mm

1. Geometric properties

Effective span of beam, L e Beam depth, H Beam spacing, Bs Flanges:

Width of timber flange element, bf Height of timber flange element, hf Web:

Thickness of the plywood web, bw Clear height between the flanges, hw Area of the web, Aw

For the I-beam, bef (equation (7.29) (EC5 9.1.1(8)))

L e = 4.0 m H = 250 mm Bs = 0.45 m bf = 45 mm hf = 50 mm bw = 12.5 mm hw = H - 2 ■ hf Aw = bw ■ H

bw 2

2. Material properties

Table 1.3, timber - strength class C18 (BS EN 338:2003, Table 1)

Characteristic bending strength, /m k

Characteristic compression strength parallel to the grain, /c 0 k

Characteristic tensile strength parallel to the grain, /t 0 k

Mean modulus of elasticity parallel to the grain, E0, mean

Table 1.13, 12.5 mm thick 5 ply Canadian softwood plywood

Characteristic compression strength,

Characteristic tensile strength,

Characteristic panel shear strength, fp.v.k

Characteristic rolling shear strength,

Mean modulus of elasticity,

Ep.c.90.mean

Mean modulus of rigidity, G w.mean fp.c.90.k = 9.7N/mm2 fp. t. 90 . k = 7.4N/mm2 fp.v.k = 3.5N/mm2 fp.r.k = 0.64 N/mm2

In the following analysis, the transformed section is based on the use of the flange material throughout the section.

Note: As the mean Evalue of the timber is greater than the mean E value of the plywood, we only need to check the bending stresses in the flange at the final condition and in the web at the instantaneous condition.

3. Partial safety factors

Table 2.8 (UKNA to BS EN 1990:2002, Table NA.A1.2(B))) for the ULS Permanent actions, yG yG = 1.35

Variable actions, yq yq = 1.5

Table 2.2 (UKNA to BS EN 1990:2002, Table NA.A1.1 - Category A

Factor for quasi-permanent value of f2 = 0.3 variable action, f2

Material factor for solid timber at the ultimate limit states (ULS), YM

Material factor for plywood web at the ULS, YpM

4. Actions

Characteristic permanent action on the beam, Gk

Characteristic variable (imposed) medium-term action on the beam,

Design load due to the critical load combination, Fd

(Table 2.8, equation (c) using the unfavourable condition variable action)

Design moment due to the critical load Md = combination, Md

Design shear force due to the critical load combination, Vd (ignoring the shear force reduction referred to in 4.5.2.1) (ii) Serviceability limit states (SLS) Design load due to permanent action at the SLS, Fsls.g

Design load due to variable action at the SLS, Fsls.q

5. Modification factors

Factor for permanent duration action and kmod service class 2, kmod.perm (Table 2.4 (EC5, Table 3.1))

Factor for medium-duration action and service class 2, kmod,med (Table 2.4 (EC5, Table 3.1))

Load sharing factor, ksys (2.3.7 (EC5, 6.6)) (n.b. 1.1 can be used if required)

Depth factor for solid timber - bending kh = min and axial tension - take the size as hf, kh (Table 2.11 (EC5, equation (3.1)) (the equation incorporates a dimensional kh = 1.25 correction factor for Mathcad)

Deformation factor for timber and kdef.f = 0.8

service class 2, kdef.f

Deformation factor for plywood and kdef.w = 1.0 service class 2, kdef.w (Table 2.10 (EC5, Table 3.2))

Buckling resistance condition with beam kc = 1 laterally supported along its compression flange, kc = 1

6. Geometric properties - transformed sections

(NB: Because the section is symmetrical about the y-y axis, the neutral axis will be at mid-depth.)

150 mm hf

0 0

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